'The Pacific': Joe Mazzello grows up on camera

When you first meet Joe Mazzello's character, Eugene Sledge, in "The Pacific," he's "18 going on 15."

"You first see him on a bicycle," Mazzello tells Zap2it in the video below. "He's just a kid."

That doesn't last long, however. Sledge -- a real-life U.S. Marine whose memoir "With the Old Breed" is part of the basis for HBO's epic miniseries -- and his fellow Marines faced some of the worst fighting in the Pacific theater of World War II, and it changed him.

It was Mazzello's job to show the effect all that fighting -- along with the miserable conditions soldiers had to endure -- had on Sledge, and the transformative effect it had on the man.

"He was a great Marine -- he was ready," Mazzello says. "But no matter how many books you read or how much boot camp you do, it's different when you get into it." Take a look:

"The Pacific," a 10-part miniseries that also stars James Badge Dale and Jon Seda, premieres Sunday (March 14) on HBO. Much more to come on the miniseries later this week.